Railway braking apparatus



Dec. 5, 1933.- J. w. LOGAN, JR

RAILWAY BRAKING APPARATUS Filed Jan. 4, 1933 INVENTOR JO/ZIZ W. Loyal JP. BY Q32 W l/[J ATTORNEY Patented Dec. 5, 1933 UNITED STATES PATENT OFFICE 1,937,768 RAILWAY BRAKING APPARATUS John W. Logan, Jr., Wilkinsburg, Pa., assignor to The UnionSwitch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application January 4, 1933. Serial No. 650,111

5 Claims.

My invention relates to railway braking apparatus, and particularly to braking apparatus of the type comprising wheel engaging braking bars located on each side of each track rail of a,

stretch of railway track, and movable toward and away from the rail into braking and non-braking positions. Moreparticularly, my present invention relates to apparatus of the type described in which the movement of the braking bars associated with each track rail into and out of their braking positions is effected by one or more operating units each of which is actuated by a fluid pressure motor.

In apparatus of the type described, and espe are provided, however,considerablediffioulty isexperienced in effecting the desired control of the valves without an excessive number of line wires. One object of-my invention is to effect the desired control of the valves, under the conditions just described with a minimum number of line wires.

Specifically, mypresent invention is designed primarily for use in controlling the supply of fluid pressure to the motors of a car retarder of the type described and claimed inan application for Let-,

ters Patent of the United States, Serial No. 516,883,

filed by Herbert L. Bone, on Feb. 19, 1931, for Railway braking apparatus, and is an improvement upon the form of control apparatus described and claimed in an application for Letters Patent of the United States, Serial No. 639,433, filed by Herbert LaBone, on Oct. 25, 1932, for Railway braking apparatus. d

I will describe one form of apparatus embodying my invention, and will then point out the novel features thereof in claims. i l l r d The accompanying drawing is a view, partly diagrammatic and partly cross-sectioned, illustrating one form of apparatus embodying my in- ,vention.

Referring to the drawing, the reference characters 1 and 2 designate the track rails of a stretch of railway track which track rails are mounted on rail 'supports 3: supported on an adjacent pairof the usual crossties 4, onlyone crosstie being visible in the drawing. Associated withthe rails i and 2 is a car retarder comp'risingtwo braking bars A and A extending parallel to rail 1 on opposite sides of this rail, and two braking bars A and A extending-parallel to, rail 2 on opposite sidesof this rail. Each of these braking bars comprises, as usual, a brake beam 5 and a brake shoe 6.

The braking bars A and A are arranged to be moved toward and away from the rail 1 by which is pivotally mounted at one end on a pin 1!) carried by the associated rail suDDQrt 3 and a lever 9 which is pivotally mounted intermediate its-ends on the pin 10. The lever B is inmeans of an operating unit comprising a lever 8 clined upwardly and extends away from the rail 1, and is providedin its upper surface with a groove 8 which receives the braking bar A Theone end Q lOf the lever 9 is likewise inclined upwardly andextends away from the rail 1 at theopposite side of the rail from the lever 8, and the other end Q of the leveri) is inclined downwardly and extends away from the rail 1 below the lever 8. The end 9 of the lever 9 is providedin its upper surface with a groove 9 similar to the groove 8 of the lever 8, which groove receives the brakingbar A The parts are so arranged and so proportioned that if the outer or free ends of the levers 8 and 9 are .movedapart, the braking bars will be moved toward :the rails into their effective or braking positions. When the braking bars occupy their braking positions, the brake shoes 6 will engage .the opposite side faces of the wheels of a car traversing the rail 1, and will retard the speed of the car. The center of gravity of thelever 8 and braking bar A is considerably to the right of the pivot'pin 10, as will be seen from an inspection of the drawing, so that this lever will normally tend to rotate in a clockwise direction about the pivot pin, Similarly, the center of gravity of-the lever 9 and braking bar A? is to 1 theleft of the pivot pin, so that this lever will normally tend to rotate in a counterclockwise direction about the pivot pin. It, will be apparent, thereforethat when no iorceis applied to the free ends of the levers 8 and 9 to move them apart, the free ends of the levers will move toward each other, thereby moving the braking bars to their open or ineffective positions in which.

they are illustrated in the drawing. i

The operating unit for moving the braking bars A and A toward and away from the rail 1 also includes a fluid pressure motor M, comprising a cylinder 11 containing a reciprocable piston 12.

which drives a piston rod 13. The cylinder 11 is pivotally connected with the free end of the lever 8 by means of trunnions 14 formed on the side of the cylinder and extending through bifurcations 15 formed on the lever 6, while the piston rod 13 is connected at its free end with the free end 9 of the lever 9 by means of an adjustable eyebolt 16 and a pivot pin 1'7. Fluid pressure may be admitted to the cylinder 11 through an opening 18 which is threaded to receive a pipe 19. mitted to the cylinder, the piston 12 is forced downwardly, and the cylinder 11 upwardly, thereby separating the levers and hence moving the braking bars toward their effective or braking positions.

The braking bars A and A are arranged to be moved toward and away from the rail 2 by means of an operating unit which is similar in all respects to that just described for moving the braking bars A and A toward and away from the rail 1, and the corresponding parts of the two units have, for the most part, been designated by the same reference characters. It will be noted, however, that ,a distinguishing exponent has been added to a few of the reference characters in order to avoid confusion in the further description of the apparatus.

The motor M is controlled by two magnet valves B and C, and the motor M is controlled by two magnet valves B and C These valves are all similar and each comprises a valve stem 20 biased to an upper position by means of a spring 21, and provided with a winding 22 and an armature 23. When valve C is energized, as shown in the drawing, valve stem 20 of this valve is moved downwardly in opposition to the bias of the associated spring 21, and under these conditions the pipe 19 communicating with the motor M is connected with atmosphere through a port 24. When valve 0 is deenergized, however, the valve stem 20 of this valve is moved to its upper position by the associated spring 21, and the pipe 19 is then disconnected from atmosphere and is connected with a pipe 25 leading to the valve B. When valve B is energized, the valve stem 20 of this valve is moved downwardly and the pipe 25 is then connected with a pipe 26 which is constantly supplied with fluid pressure, usually air, from a suitable source not shown in the drawing, but when valve B is deenergized, the pipe 25 is then disconnected from the pipe 26. It will be apparent, therefore, that when valve C is energized, fluid pressure is exhausted from the motor M, and that when valve C is deenergized and. valve B is energized, fluid pressure is admitted to the motor M. l

The valves B and C control the supply of fluid to, and exhaust of fluid from, the motor M in exactly the same manner as the valves B and C control the supply of fluid to, and exhaust of fluid from the motor M, and the operation of these latter valves will, therefore, be readily understood from an inspection of the drawing without further description.

The valves B and C are controlled in part by a plurality of pressure responsive devices P P and P each comprising a Bourdon tube 28 connected to the pipe 19, and hence subjected to the pressure of the fiuid in the region of cylinder 11 between the piston 12 and the upper end of' the cylinder. Each Bourdon tube 28 controls two contacts 2'7-27 and 27-27 The pressure responsive devices P P and P are so constructed that they will operate successively When fluid pressure is ad-' as the pressure of the fluid in the motor M increases. For example, for all pressures below 20 pounds per square inch, contact 27-27 of each of these devices is closed. If the pressure exceeds 20 pounds per square inch, however, contact 27-27 of pressure responsive device 1 opens, and if the pressure exceeds 30 pound per square inch, contact 27-27 of pressure responsive device P closes. In similar manner, the pressure responsive devices P and F are adjusted to open their contacts 2'7-27 at 45 and 70 pounds per square inch, respectively, and to close their contacts 2'7-2'7 at 55 and pounds per square inch, respectively. Of course, these specific pressures are not essential but are only mentioned for purposes of explanation.

The valves B and C are each controlled in part by a plurality of pressure responsive devices which are similar in all respects to those just described for controlling the valves B and C, and which are each designated by a corresponding reference character with a suitable distinguishing subscript, the Bourdon tube 23 of each of these devices being connected with the pipe 19 which communicates with the upper end of cylinder 11 of motor M The valves B, C, B and C are also each controlled in part by a manually operable lever L comprising a contact arm 29 movable into engagement with a selected one, or ones, of a plurality of fixed contacts designated by the referencecharacters 30 to 34, inclusive.

As shown in the drawing, lever L occupies its off position in which contact 29-30 is closed.

Under these conditions, all circuits for the valves wire 35, an asymmetric unit 8 in its low resist- 1..

ance direction, wire 42, winding 22 of valve C wire 43, and line wire 40 back to battery D. The valves B and B are therefore both deenergized, and the valves C and C are both energized.

Since the valves B and B are deenergized, the

supply of fluid pressure to both of the motors M and M is cut off, and since the valves C and C are energized, the motors M and M are each connected with atmosphere. The braking bars are therefore held in their braking positions by gravity. The contacts 27-27 of the pressure responsive devices P and P1 are all closed, and the contacts 2'7-2'7 of these devices are all open.

I will now assume that lever L is moved from the position in which contact 29-30 is closed to the position in which contact 29-31 is closed. Under these conditions, the valves C and C both become deenergized, and the valve B becomes energized over a circuit which passes from battery D through contact 29-31 of lever L, line wire 44,

wire 45, an asymmetric unit S in its low resistance direction, contact 27-27 of pressure responsive device P wires 47 and 48, winding 22 of valve B, wire 39, and line wire 40 back to battery D.

The valve B now also becomes energized over a circuit which passes from battery D through contact 29-31 of lever L, line wire 44, an asymmetric unit S in its low resistance direction, contact 27-2'7 of pressure responsive device P1 wires 50 and 51, winding 22 of valve B wire 43, and

ill

. sponsive device P opens.

:line wire 40 back to battery D. The 'deenergization of valve C disconnects the motor M from atmosphere, while the energization of valve B ad- .mits fluid pressure to this motor, so that the braking bars A and A are nowmoved to their braking positions; When the pressure of the fluid in the motor M reaches pounds per square inch,

contact 27-27 of pressure responsive device Pmr opens and deenergizes valve B, thus preventing further supply of fluid to the motor M unless the pressureagain decreases to that at which contact 27-27 of pressure responsive device P closes. If the pressure of the fluid in motor M now increases beyond :30pounds per square inch for any reason, a circuit will become responsive device P wires 52 and 38, winding 22 of valve C, wire 39, andline wire back to battery D. Valve C willtherefore now become energized and will v'entfluid frommotor M to atmosphere until thepressure again decreases to that at which contact 27-27 of pressure re- In a similar manner, the deenergization of valve C disconnects ..motor M from atmosphere, while the energizetion of valve 13 admits fluid to this motor. When the pressure of the fluid in motor M increases :to that at which contact 27-27 of pressure rea sponsive device PR opens, valve B will again becomedeenergized, and thepressure of the fluid increases to 30 pounds per square inch,a

circuit will become completed for'valve. B 'at contact 27-27 of pressure responsive device P1 so that this valve will then becomeener- .gized and will exhaust fluid from the motor M to atmosphere. The circuit-which becomes completed for valve B at contact 27-27? of pressure responsive device P1 under the conditions .just described may be traced from battery D through contact 29-31 of lever L, line wire 44,

asymmetric unit S inits low resistance direction, contact 27-2'7 of pressure responsive device both sets of braking bars will be moved to their braking positions by a pressure of between 20 and 30 pounds per square inch. 7

If the operator moves lever L to theposition in which contact 29-32, is closed, valve B will,

become energized and will admit fluid to motor M until the pressure of the fluid in the motor increases to pounds per square inch, the circuit for valve B, under these conditions, passing from battery D through contact 29-32 of lever FW- wires 59, 52 and 38, winding 22 of valve '0, wire 39, and line wire 40 back to battery D.

L, line wire 53, wire 54, an asymmetric unit S in its low resistance direction, contact. 27-27 of pressure responsive device P wires 56, 47

.and 48, winding 22 of valve B, wire 39, and line wire 40 back to battery D. At the same, time valve B will become energized and will admit a fluid to motor, M until the pressure in thismotor increases to 45 pounds per square inch, the circuit for this latter valve passing from battery D through contact 29-32 of lever L, line wire 53, an asymmetric unit S in its low resistance direction, contact 27-2? of pressure responsive device P1 "wires 58, 50 and 51, winding 22 of valve B wire 43, and line wire 40 back to battery D. If the pressure of the fluid in motor M now increases to pounds per squareinch,

sure pounds, the circuit for valve C under these conline wire 40 back to battery D.

fluidfrom motor M to atmosphere until the presin the motor again decreases below 55 ditions passing from battery D through contact 29-32 of lever L, line wire 53, wire 54, asymmetric unit S in its low resistance direction,

contact 27-27 of pressure responsive device P5 wires ,59, 52 and 38, winding 22 of valve '0, wire 39, and line wire 40 back to battery D.

:again decreases below 55 pounds, the circuit for;

the valve C vunder these conditions passing from battery D through contact 29-32 of lever L, line wire 53, asymmetricunit S in its low resistance direction, contact 27-27 of pressure responsive device P1 ,'wires 60, 52 and 42, winding 22 of U valve C ,,wire 43, and line wire 40 back to battery D. It will be apparent, therefore, that when lever L occupies the position in which contact 29-32 is closed,fluid at a pressure of between 45 and 55 pounds per square inch will be supplied. to both of the motors M and M and the braking bars will be held in their braking positions by, a

corresponding pressure.

If the operator moves lever L to the position in which contact 29-33 is closed, the valves II- and B will again become energized and will now remain energized until the pressure in thernotors M and M increases to poundsper square. inch. The circuit over which valve B becomes energized under these conditions may be traced from battery D through contact 29-33 of lever L, linewire 61, wire 62, an asymmetric unit S in its lowresistance directiongcontact 27-27" of pressure responsive device F wires 56, 47 and 48, winding 22 of valve B, wire 39, and line wire 40 back to battery D, while the circuit over "which valve 13 becomes energized may be traced from battery D through contact 29-33 of, lever L, line Wire 61, an asymmetric unit S in its low resistance direction, contact 27-2"! of pressur: responsive device P1 q wires 58, 50 and 51, winding 22of valve B wire43, and linewire40 back to battery D. If, with lever L in the position in which contact 29-32 is closed, the pressure of the fluid in motor M increases to 8C1 pounds per square inch, valve 0 will become energized and will exhaust fluid pressure from this motor until the pressure in the motor again decreases to 80 pounds per square inch, the circuit over which valve C becomes energized under these conditions passing from battery D through contact 29-33 of lever L, line wire 61, wire 62,

asymmetric unit S in its low resistance direction,

contact 27-27 of pressure responsive device Likewise, when lever L occupies the position in which contact 29-33 is closed, if the pressure of the fluid in motor M increases to 80 pounds per square inch, valve C will become energized and will exhaust fluid from this latter motor until the pressure again decreases below 80 pounds, the circuit for valve C passing from battery D through contact 29-33 of lever L, line wire 61, asymmetric unit S contact 27-27 of pressure responsive device P1 wires 60, 52 and 42, winding 22 of valve C wire 43, and It will be seen therefore that when contact 29-33 of lever L valve C will become energizedand will exhaust V is: closed, the braking bars will be held in their,

'sive device P1 braking positions by a pressure of between 70 and pounds per square inch.

If lever L is moved to the position in which contact 2934 is closed, the valves B and B will become energized and will remain energized so that fluid at full line pressure will then be supplied to the motors M and M The circuit for valve B, under these conditions, passes from battery Dthrough contact 29-34 or" lever L, line wire 65, wire 66, an asymmetric unit S in its low resistance direction, wire 48, winding 22 of valve B, wire 39, and line wire 46 back to battery D. The circuit for valve B under these conditions passes from battery D through contact 29-434 of lever L, line wire 65, asymmetric unit S in its low resistance direction, wire 51, winding 22 of valve B wire 43, and line wire 40 back to battery D. It will be apparent therefore that when lever L occupies the position in which contact 2934 is closedgthe braking bars are held in their braking positions by fluid at full line pressure.

It should be observed that if the operator moves the lever L from a position corresponding to a higher braking force to a position corresponding to a lower braking force, the apparatus immediately and automatically reduces the braking pressure exerted by both operating units to a value corresponding to the new position of the lever in a manner which will be apparent from from the drawing without tracing the sequence of the operation in detail.

In order to restore the braking bars to their open or ineflective positions when they are in their closed or effective positions, the operator moves lever L tothe position in which contact 2930 is closed, in which position it is illustrated in the drawing. Under these conditions, all circuits for the valves B and B become opened so that both of these valves become deenergized, and the circuits which were previously traced for the valves C and C including contact 29-30 of lever L becomes closed so that these latter valves both become energized. The deenergization of the valves B and B cuts off the supply of fluid pressure to the motors M and M respectively, while the energization of the valves C and C connects the motors M and M with atmosphere, thereby exhausting the fluid which was previously supplied to the motors from the motors. The brakings bars A A A and A therefore now return to the ineffective or non-braking positions by gravity. When the braking bars reach their non-braking positions, all parts are then re stored to the positions in which they are illustrated in the drawing.

It should be particularly pointed out that the function of the asymmetric units S to S is to prevent improper operation of the control valves due to feed back of current from one group of valves to the other group. For example, I will assume that lever L occupies the position in which contact 2932 is closed, and that the pressure in motor M increases to 55 pounds per square inch, so that contact 2727 of pressure responbecomes closed. Under these conditions, if it were not for the asymmetric unit S current would flow from battery D through contact 29-32 of lever L, line wire 53, asymmetric unit S in its low resistance direction, contact 2'7--2'7 of pressure responsive device P1 wires 60, 52 and 36, asymmetric unit S wire 38, winding 22 of valve C, wire 39, and line wire 40 back to battery D, thus energizing valve C, and hence exhausting fluid from motor M regardless of the pressure of the fluid in this latter motor, which operation is obviously undesirable. As another example of the function of these units, when lever L is initially moved to the position in which contact 29-34 is closed, and the pressure in the two motors M and M is building up to line pressure, a time might occur when contact 2'72'7" of pressure responsive device P1 is still closed after contact 2727 of pressure responsive device P has become closed, and under these conditions, if it were not for the asymmetric unit S valve 0 would become improperly energized over a circuit which may be traced from battery D through contact 2934 of lever L, line wire 65, asymmetric unit S in its low resistance direction, wires 50 and 58, contact 272'7 of pressure responsive device P170 80, wire 62, asymmetric unit S in its low resistance direction, contact 2'72'7 of pressure responsive device F wires 59, 52 and 88, winding 22 of valve C, wire 39, and line wire 40 back to battery D. In a similar manner, each of the other units functions under other similar conditions to prevent feed-back from one set of valves to the other.

It should also be pointed out that while for purposes of describing my invention, I have shown only one operating unit for each pair of braking bars, and a separate set of valves for controlling the fluid pressure motor of each unit, in actual practice each pair of braking bars will be provided with a plurality of other operating units disposed at intervals along the bars substantially as shown in the Bone application Serial No. 516,883, referred to hereinbefore, and each set of valves will be utilized to control a group of the motors for these units, as many additional sets of valves being provided as are necessary to handle the necessary volume of fluid for the desired number of motors. When additional sets of valves are provided, the motors may be grouped in the most convenient manner and the valves of each set may be connected to the line wires 35,

65, 44, 53, 61 and 40 in substantially the same manner as the valves of either of the sets of valves shown in the drawing are connected with these line wires, it being obvious that when the additional valves are connected with the line wires in the same manner as those shown in the drawing, their operation will be similar to that previously described for either group of valves shown in the drawing.

Although I have herein shown and described only one form of railway braking apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is: I

1. In combination, a plurality of fluid pressure actuated car retarder operating motors, a series of normally closed pressure responsive contacts for each motor subject to the pressure of the fluid in the associated motor and arranged to operate successively as the pressure of the fluid in the associated motor increases, a series of normally open contacts for each motor subject to the pressure of the fluid in the associated motor and one provided for each of said normally closed contacts and each arranged to become closed when the pressure in the associated motor increases to a' pressure which is somewhat higher than the pressure at which the corresponding normally closed contact opens, a first magnet valve for each motor for controlling the admismotor between said common line wire and each of the remaining line wires over a difierent one of the normally closed contactsyassociated with such motor, means for connecting the second magnet valve for each motor between Mid common line wire and each of the remaining line wires over a different one of the normally open contacts associated with such motor, and for preventing the Valves associated with motor from becoming improperly energised due l to operation of the contacts associated with the valves for any other motor.

2. In combination, a plurality of fluid pressure actuated car retarder .operatingmotors, a series of normally closed pressure responsive contacts for each motor subject to the pressure of the fluid in the associated motor and arranged to operate successively as the pressure of the fluid in 'the associated motor increases, a series of normally open contacts for each motor subject to the pressure of the fluid in the associated motor and one provided for each of said normally closedcontacts and each arranged to become closed when the pressure in the associated motor increase to a pressure which is somewhat higher than the pressure at whichthe corresponding normally closed contact opens, "a first magnet valve for each motor for controlling the admis-- sion of fluid to the associated motor, a second magnet valve for each motor forcontrolling the exhaust of fluid from the associated motor, a common line wire and a plurality of other line wires, means for selectively connecting a source of electromotive force between said common line wire and each of the remaining line wires, means for connecting the first magnet valve for each motor betweensaid common line wire and each of the remaining line wires over a different one of the normally closed contacts associated with such motor, means for connecting the second magnet valve for each motor between said common line wire and each of the remaining line wires over a different one of the normally open contacts associated with such motor, and an asymmetric unit interposed in the connection between each valve and each line wire in such manner that current is prevented from flowing from a line wire which is connected with the source through the pressure responsive contacts associated with one motor, another line wire, the pressure responsive con tacts associated with another motor, and the winding of one of the valves associated with such other motor back to the common line wire, whereby improper energization of the valves associated with each motor is prevented. I

3. In combination, a first and a second fluid pressure actuated car retarder operating motor, a first magnet valve for controlling the admisto the pressure of the fluid-in said first motor and adjusted to become opened successively as the pressure in said first motor increases, second and third pressure responsive contacts subject to the pressure of the fluid in said first motorand so adjusted that said third contact will become closed at a somewhat higher pressure than the pressure at which said first contact opens and that said fourth contact will become. closed at a somewhat higher pressure than the pressure at which said second contact opens, fifth andsixth pressure responsive contacts subjected to the pressure of the fluid in said second motor and adjusted to become opened successivelyas the pressure in said second motor increases, seventh and eighth pressure responsive contacts subjected to the pressure of the fluid in said second motor and so adjusted that said seventh contact will become closed at a somewhat higher pressure than the pressure at which said fifth contact opens and that said eighth contact will become closed at a somewhat higher pressure than the pressure at which said sixth contact opens, first, second and third wires; means for selectively connecting a source of electromotive force between said first and said second wires and between said first and said third. wires, four asymmetric units, means including a first one .of said asymmetric units and said first contact for connecting said first magnet valve with said first and second line wires, means includinga second one of said asymmetric units and said second contact for connecting said first magnet valve withsaid first and third line wires, means including said first asymmetric unit and said third contact for connect-' ing said second magnet valve with said first and second line wires,,means including said second asymmetric unit and said fourth contact for conmeeting said second magnet valve with said first and third line wires, 'means including a third one of said asymmetric units and said fifth contact for connecting said third magnet valve with said first and second line wires, means including the fourth asymmetric unit and said sixth contact for connecting said fourth magnet valve with said first and third line wires, means including said third asymmetric unit and said seventh contact for connecting said third magnet valve with said first and second line wires, and means including said fourth asymmetric unit and said eighth contact for connecting said fourth magnet valve with said first and third linewires, said asymmetric units all being disposed in the same direction with respect to said first line wire.

4. In combination, a first and a second fluid pressure actuated car retarder operating motor, a first magnet valve for controlling the admission of fluid to said first motor, a second magnet valve for controlling the exhaust of fluid from said first motor, a third magnet valve for controlling the admission of fluid to said second motor, a fourth magnet valve for controlling the exhaust of fluid from said second motor, a first normally closed contact responsive to the pressure of the fluid in said first motor and adjusted to open at a predetermined pressure, a first normally open contact responsive to the pressure of the fluid in said first motor and adjusted to become closed at a pressure which is somewhat higher than the pressure at which said first contact opens, a second normally closed contact responsive to the pressure of the fluid in said second motor and adjusted to open at a predetermined pressure, a second normally open contact responsive to the pressure of the fluid in said second motor and adjusted to become closed at a pressure which is somewhat higher thanthe pressure at which said second normally closed contact opens;- first, second andthird line wires; means for selective- 1y supplying current to said first and said secs ond line wires and to said first and said third line wires, four asymmetric units, means includ: ing a first one of said asymmetric units and said first normally closed contact for connecting said first valve with said first and second line wires, means including said first asymmetric unit and said first normally open contact'for connecting said second magnet valve with said first and sec, ond line wires, means including a second one of said asymmetric units and said second normal-w ly closed contact for connecting said third magnet valve withsaid first and second line wires, means including said second asymmetric unit an said second normally open contact for connecting said fourth magnet valve with said first and second line wires, means including a third one of said asymmetric units for connecting said first magnet valve with said first and third line wires, and means including the remaining asymmetric units for connecting said third magnet valve directly with said first and third line wires, said asymmetric units all being disposed in the same direction with respect to said first line wire.

5. In combination, a first and a second fluid pressure actuated car retarder operating motor, a first magnet valve for controlling the admission of fluid to said first motor, a second magnet valve for controlling the exhaust of fluid from said first motor, a third magnet valve for controlling the admission of fluid to said second motor, a fourth magnet valve for controlling the exhaust of fluid from said second motor, a first normally closed contact responsive to the pressure of the fluid in said first motor and adjusted to open at a predetermined pressure, a first normally open contact responsive to the pressure of the fiuid in said first motor and adjusted to become closed at a pressure which is somewhat higher than the pressure at which said first contact opens, a second normally closed contact responsive to the pressure of the fluid in said second motor and adjusted to open at a predetermined pressure, a second normally open contact responsive to the pressure of the fluid in said second motor and adjusted to become closed at a pressure which is somewhat higher than the press sure at which said second normally closed con' tact opens; first, second and third line wires; means for selectively supplying current to said first and said second line wires and to said first and said third line wires, four asymmetric units, means including a first one of said asymmetric units and said first normally closed contact for connecting said first valve with said first and sec-. ond line wires, means including said first asymmetric unit and said first normally open contact for connecting said second magnet valve with said first and second line wires, means including a second one of said asymmetric units and said second normally closed contact for connecting 1E3 said third magnet valve with said first and sees ond line wires, means including said second asymmetric unit and said second normally open con tact for connecting said fourth magnet valve with said first and second line wires, means including a third'one of said asymmetric units for connecting said second magnet valve with said first and third line wires, and means including the remaining asymmetric units for connecting said fourth magnet valve directly with said first lie and third line wires, said asymmetric units all being disposed in the same direction with respect to said first line wire.

JOHN W. LOGAN, JR. 

